There are a number of existing brake control systems for facilitating the control of motor vehicles on slopes.
EP 0 784 551 B1 discloses a brake control system comprising a hill descent mode in particular for vehicles used in off-road conditions. The brake control system comprises an electronic control unit and a brake control system to control brakes associated with each wheel of the vehicle. A driver interface in the form of a switch is used to cause the control unit to enter a hill descent mode when the vehicle is also detected to be in gear. In this mode the control unit controls the speed of the vehicle by braking to slow the vehicle when a detected vehicle speed is above a preset target speed.
When driving a motor vehicle off road it might be necessary to come to a standstill on a slope. In this context, EP 1 777 133 A1 discloses a brake control system in which a brake control means is arranged to detect when the vehicle is stationary and is held on a slope by a braking effort supplied by brakes in accordance with the operation of a brake command means (such as a brake pedal). The release of the braking effort is controlled as a function of the steepness of the slope following operation of the brake command means to release the brakes.
Whilst the brake control system of EP 1 777 133 A1 helps to smooth transition from a stationary position to hill descent to a degree, it does not exercise control over the vehicle once it is in hill descent. The system of EP 1 777 133 A1 may of course be used in conjunction with the system of EP 0 784 551 B1, but this can still lead to jerky (and therefore, to a degree, uncontrolled) hill descent in some circumstances, for example if the vehicle gathers speed following the release of the brakes by the system of EP 1 777 133 A1 and then has to be braked heavily when the target speed of the system of EP 0 784 551 B1 is exceeded.
It is an aim of this invention to provide an improved brake control system that overcomes or minimises the above problem. Other aims and advantages of the invention will become apparent from the following description, claims and drawings.